with clown it's very easy to tell if they have paired. Mine started fighting a few weeks after I added them to the tank and constantly chasing each other around the tank.
When they start paring, the male (Usually the smallest one), starts doing this little spasm like moves next to the female. This is a sign that he is submitting to her. Once that goes on for a few weeks, they stop and can be considered paired.
I'm sure others here with much more knowledge and experience than me can give you some more accurate and scientific ways, but if they are not fighting all the time, they are more than likely paired.
Right, I'm familiar with the whole process. My clowns were about the same size ehen I first got them (in July) now the female is noticeably bigger. The male started submitted (spazzing) and 2 weeks after I got them. Like I said for the most part there fine but every now and then the female will put him in his place...nothing too crazy.
The only reason I thought they weren't a pair is because I thought when they paired there was no aggression at all and they would not ever get too far away from each other. Maybe this isn't always the case though?